The present invention relates to a semiconductor structure used in sensors for sensing dynamic quantities. The present invention relates also to a method of manufacturing the semiconductor structure.
At first, conventional methods of manufacturing a semiconductor structure are explained with reference to FIGS. 6(a) through 8(f).
FIGS. 6(a)-6(e) describe a first conventional method of manufacturing a semiconductor structure.
Referring now to FIGS. 6(a)-6(e), an insulation layer 11 of boro-phospho silicate glass (BPSG) or phospho silicate glass (PSG) is formed on an Si substrate 10 in the step shown in FIG. 6(a). A polysilicon layer 12, that will be a movable electrode and a stationary electrode later, is formed on the insulation layer 11. Alternatively, silicon on an insulator (hereinafter referred to as xe2x80x9cSOIxe2x80x9d) wafer, including an oxide insulation layer 11 bonded onto the Si substrate 10 and the Si active layer 12 on the oxide insulation layer 11, is used.
In the step of FIG. 6(b), a resist film is formed on the polysilicon layer (or the Si active layer) 12, and the resist film is patterned. Then, the polysilicon layer (or Si active layer) 12 with the patterned resist film thereon is etched, resulting in a sensor structure 13.
In the step of FIG. 6(c), the oxide insulation layer 11 or sacrificed layer, such as the BPSG insulation layer, PSG insulation layer, or Si oxide layer, is etched with buffered hydrofluoric acid (BHF) or such an etchant 20.
Thus, a polysilicon structure 30 including the deformable sensor structure 13 formed of Si beams is formed above the central part of the substrate 10. The polysilicon structure 30 is spaced apart from the Si substrate 10 in the central part of the Si substrate 10. The polysilicon structure 30 is sustained by the beams on the Si substrate 10 in the peripheral part of the Si substrate 10.
In the step of FIG. 6(d), the etchant 20 is replaced by a cleaning liquid, such as pure water and isopropyl alcohol (IPA), and the region including the polysilicon sensor structure 13 is washed with the cleaning liquid.
In the drying step of FIG. 6(e), surface tension 21 of the cleaning liquid occurs in the gap between the sensor structure 13 and the Si substrate 10. The sensor structure 13 with low rigidity is attracted to the Si substrate 10 by the surface tension 21.
FIGS. 7(a)-7(h) describe a second conventional method of manufacturing a semiconductor structure.
Referring now to FIG. 7(a), an insulation layer 11 of BPSG or PSG is formed on a Si substrate 10. A polysilicon layer 12, that will be a movable electrode and a stationary electrode later, is formed on the insulation layer 11. Alternatively, an SOI wafer, including an oxide insulation layer 11 bonded onto an Si substrate 10 and an Si active layer 12 on the oxide insulation layer 11, is used.
In the step of FIG. 7(b), a resist film is formed on the polysilicon layer (or Si active layer) 12, and the resist film is patterned. Then, the polysilicon layer (or Si active layer) 12 with the patterned resist film thereon is etched, resulting in a sensor structure 13.
In the step of FIG. 7(c), a sacrificed layer (BPSG insulation layer, PSG insulation layer, or Si active layer) is etched with an etchant 20 to an extent that the sensor structure 13 does not become completely free.
In the step of FIG. 7(d), the sensor structure 13 and the sacrificed layer remaining under the sensor structure are covered with a photosensitive polymer film 40, and the photosensitive polymer film 40 is patterned so that the sensor structure 13 is sustained by the patterned photosensitive polymer film.
In the step of FIG. 7(e), the remaining sacrificed layer is etched and the resulting sensor structure 13 is dried. Since the sensor structure 13 is sustained by the rigidity of the photosensitive polymer 40, any sticking phenomenon does not occur between the sensor structure 13 and the substrate 10.
In the step of FIG. 7(f), the photosensitive polymer 40 is removed by ashing or such a dry process.
The sensor structure 13 is made free and deformable through the steps of FIGS. 7(g) and 7(h).
FIGS. 8(a)-8(f) describe a third conventional method of manufacturing a semiconductor structure disclosed in Japanese Unexamined Laid Open Patent Publications No. H07-209105 and No. H07-245414.
Referring now to FIG. 8(a), an insulation layer 11 of BPSG or PSG is formed on an Si substrate 10. A polysilicon layer 12, that will be a movable electrode and a stationary electrode later, is formed on the insulation layer 11. Alternatively, an SOI wafer, including an oxide insulation layer 11 bonded onto the Si substrate 10 and the Si active layer 12 on the oxide insulation layer 11, is used.
In the step of FIG. 8(b), a resist film is formed on the polysilicon layer (or Si active layer) 12, and the resist film is patterned. Then, the polysilicon layer (or Si active layer) 12 with the patterned resist film thereon is etched, resulting in a sensor structure 13.
In the step of FIG. 8(c), the insulation layer 11 or sacrificed layer (BPSG insulation layer, PSG insulation layer, or Si active layer) is etched with BHF or such an etchant 20.
In the step of FIG. 8(d), the etchant is replaced by a sublimable material 50, such as paradichlorobenzene and naphthalene, in the liquid state thereof. The sublimable material 50 is solidified in the gap between the sensor structure 13 and the Si substrate 10.
The sensor structure 13 is formed finally through the steps of FIGS. 8(e) and 8(f) by sublimating the sublimable material 50.
The conventional semiconductor structures or the conventional methods of manufacturing the semiconductor structures have the problems described below.
As described in connection with the steps of FIGS. 6(d) and 6(e) in the first conventional manufacturing method, the surface tension 21 of the cleaning liquid occurs in the gap between the polysilicon structure 30 and the Si substrate 10. The sensor structure 13 with low rigidity is attracted to the Si substrate 10 by the surface tension 21, to cause the sticking phenomenon.
In the second conventional manufacturing method described with reference to FIGS. 7(a)-7(h), it is difficult to precisely pattern the photosensitive polymer film 40 on the condition that unevenness of several xcexcm is caused by the etching of the first sacrificed layer. It is also difficult to inject equally the photosensitive polymer down to the bottom surfaces of the trenches etched through the sacrificed layer.
Furthermore, it is difficult to completely remove the photosensitive polymer film 40 by ashing or such a dry process, causing low throughput for the manufacture. The incomplete removal of the photosensitive polymer film 40 is hazardous for securing the deformable range of the sensor structure 13, causing a sensor with low reliability.
The second conventional manufacturing method increases the manufacturing costs, since the sacrificed layer is etched through two isolated steps and the step of burning (ashing) the photosensitive polymer film 40 is added.
According to the third conventional manufacturing method, the sublimable material 50 is not removed completely, remaining as foreign substances on the clean sensor surface. The remaining foreign substances impair the reliability of the sensor.
In view of the foregoing, it is an object of the invention to provide a highly reliable semiconductor structure.
It is another object of the invention to provide a method of manufacturing a reliable semiconductor structure, that facilitates, without employing any special step, preventing sticking phenomena, improving the throughput and reducing the manufacturing costs.
According to an aspect of the invention, there is provided a semiconductor structure including: a substrate; a deformable beam structure above the substrate; and convexities on the lower surface of the deformable beam structure, the convexities with the tips extending to point to the substrate. The tips of the convexities and the substrate are spaced apart widely enough to provide the deformable beam structure with a predetermined deformable range.
Advantageously, the convexities are formed beneath a portion of the deformable beam structure where the largest deformation is formed, or beneath portions of the deformable beam structure where the deformations thereof are relatively large.
According to another aspect of the invention, there is provided a semiconductor structure including: a tertiary laminate including a first layer formed of a silicon substrate, a second layer on the first layer formed of an insulation layer, and a third layer on the second layer formed of a silicon layer; and a deformable beam structure in the third layer including device elements wired on the third layer, weight sections having a plurality of through holes bored through the third layer, beam sections sustaining the weight sections and having sensor elements wired on the third layer for detecting displacements, and convexities remaining on the lower surfaces of the weight sections with the tips thereof pointing to the first layer after etching off the second layer through the through holes of the third layer.
According to a further aspect of the invention, there is provided a method of manufacturing a semiconductor structure including a substrate and a deformable beam structure above the substrate. The method includes the steps of: preparing a laminate formed of the substrate, an insulation layer on the substrate, and an active layer on the insulation layer; wiring functional devices on the active layer; forming etching trenches in the active layer down to the insulation layer; etching off the insulation layer with an etchant injected into the etching trenches to form the deformable beam structure; and adjusting the period of time for the etching off to form convexities extending from the deformable beam structure with the tips thereof pointing to the substrate and to space apart the tips of the convexities and the substrate from each other widely enough to provide the deformable beam structure with a predetermined deformable range.
Advantageously, the convexities are formed beneath the portion of the deformable beam structure where the largest deformation is caused, or beneath the portions of the deformable beam structure where the deformations are relatively large.
According to a still further aspect of the invention, there is provided a method of manufacturing a semiconductor structure. The method includes the steps of: preparing a laminate including a first layer formed of a silicon substrate, a second layer formed of an insulation layer, and a third layer formed of a silicon active layer; wiring functional devices on the third layer; forming etching trenches in the third layer down to the second layer; etching off the second layer through the etching trenches to form a deformable beam structure, the deformable beam structure including weight sections and beam sections sustaining the weight sections, the beam sections including sensor elements for detecting displacements; and adjusting the period of time for the etching off to form convexities extending from the weight sections with the tips thereof pointing to the first layer.